CCAAT/enhancer-binding protein α (C/EBPα, C/EBP alpha or C/EBPA) is a leucine zipper protein that is conserved across humans and rats. This nuclear transcription factor is enriched in hepatocytes, myelomonocytes, adipocytes, as well as other types of mammary epithelial cells [Lekstrom-Himes et al., J. Bio. Chem, vol. 273, 28545-28548 (1998)]. It is composed of two transactivation domains in the N-terminal part, and a leucine zipper region mediating dimerization with other C/EBP family members and a DNA-binding domain in the C-terminal part. The binding sites for the family of C/EBP transcription factors are present in the promoter regions of numerous genes that are involved in the maintenance of normal hepatocyte function and response to injury. C/EBPα has a pleiotropic effect on the transcription of several liver-specific genes implicated in the immune and inflammatory responses, development, cell proliferation, anti-apoptosis, and several metabolic pathways [Darlington et al., Current Opinion of Genetic Development, vol. 5(5), 565-570 (1995)]. It is essential for maintaining the differentiated state of hepatocytes. It activates albumin transcription and coordinates the expression of genes encoding multiple ornithine cycle enzymes involved in urea production, therefore playing an important role in normal liver function.
In the adult liver, C/EBPα is defined as functioning in terminally differentiated hepatocytes whilst rapidly proliferating hepatoma cells express only a fraction of C/EBPα [Umek et al., Science, vol. 251, 288-292 (1991)]. C/EBPα is known to up-regulate p21, a strong inhibitor of cell proliferation through the up-regulation of retinoblastoma and inhibition of Cdk2 and Cdk4 [Timchenko et al., Genes & Development, vol. 10, 804-815 (1996); Wang et al., Molecular Cell, vol. 8, 817-828 (2001)]. In hepatocellular carcinoma (HCC), C/EBPα functions as a tumor suppressor with anti-proliferative properties [Iakova et al., Seminars in Cancer Biology, vol. 21(1), 28-34 (2011)].
Different approaches are carried out to study C/EBPα mRNA or protein modulation. It is known that C/EBPα protein is regulated by post-translational phosphorylation and sumoylation. For example, FLT3 tyrosine kinase inhibitors and extra-cellular signal-regulated kinases 1 and/or 2 (ERK1/2) block serine-21 phosphorylation of C/EBPα, which increases the granulocytic differentiation potential of the C/EBPα protein [Radomska et al., Journal of Experimental Medicine, vol. 203(2), 371-381 (2006) and Ross et al., Molecular and Cellular Biology, vol. 24(2), 675-686 (2004)]. In addition, C/EBPα translation can be efficiently induced by 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO), which alters the ratio of the C/EBPα protein isoforms in favor of the full-length p42 form over p30 form thereby inducing granulocytic differentiation [Koschmieder et al., Blood, vol. 110(10), 3695-3705 (2007)].
The C/EBPα gene is an intronless gene located on chromosome 19q13.1. Most eukaryotic cells use RNA-complementarity as a mechanism for regulating gene expression. One example is the RNA interference (RNAi) pathway which uses double stranded short interfering RNAs to knockdown gene expression via the RNA-induced silencing complex (RISC). It is now established that short duplex RNA oligonucleotides also have the ability to target the promoter regions of genes and mediate transcriptional activation of these genes and they have been referred to as RNA activation (RNAa), antigene RNA (agRNA) or short activating RNA (saRNA) [Li et al., PNAS, vol. 103, 17337-17342 (2006)]. saRNA induced activation of genes is conserved in other mammalian species including mouse, rat, and non-human primates and is fast becoming a popular method for studying the effects of endogenous up-regulation of genes.
Thus, there is a need for targeted modulation of C/EBPα for therapeutic purposes with saRNA.